Nest Thermostat (Mirror) Reading 20° high ambient Temperature. Reads correct when calling for heat.

[G-OFFree]

Nest Thermo (mirror style) ambient temp is reading 20° F high when idle. If you adjust temp to call for heat ambient temp drops to correct reading slowly. 20-30 seconds per degree. 
once temp equalizes (stops calling for heat) ambient temperature rises at the same rate. 
troubleshooting so far 

restart - 3 times

factory reset - twice

replace batteries - once

check wiring - twice

yell obscenities - many

its been installed for over a year. New issue today. 
if there’s an idea I’d love to here it. Otherwise I’m thinking it’s junk. 

[Markjosephp]

Hello G-OFFree,

It sounds like you've gone through quite a troubleshooting journey with your Nest Thermostat. I understand your frustration when these issues pop up, especially after a year of smooth operation.

Given the comprehensive steps you've already taken, it might be worth it if you could take a photo of the thermometer next to your Nest Thermostat. Both the thermometer and thermostat screens should be visible in the photo and show the difference in each other's readouts. Also, make sure the software version is up-to-date.
 

Feel free to share any updates or additional details if you have them.

Regards,
Mark

[G-OFFree]

Hi Mark,

a follow up email was sent regarding the use of a 2nd transformer. Unfortunately, the Google power adapter is not compatible with my system. End result is I now have a new Nest paperweight. It’s very sad that after a year of operation an update or “adjustment” on the software has caused the failure. 

[Markjosephp]

Hey there,

Thanks for the details. Can you share with us your thermostat's software version? 

Keep me posted.

Regards,
Mark

[Amyg]

I am also having the same issue on our vacation home.  It’s imperative that it reads correctly so that the heat turns on and the pipes don’t burst.  But the thermostat says it’s 80 in the house and there is no way it’s even close to that (20°lower).   Tried everything above including checking for software update.  Please help! Otherwise this is a useless product.  

[G-OFFree]

Hi, a follow up email was sent to me stating that you have to use only the “Google” supplied power adapter. The following is the email. Needless to say the Google adapter is not compatible with my system so I now have a new Nest paper weight. 

We’ve identified an issue with the installation of your new nest t-stat. If you plugged a second transformer into a wall outlet to provide power to your thermostat, please remove it to prevent permanent damage. Installing a second transformer can lead to hardware failure and could jeopardize your warranty. When your hardware fails, you will likely experience:

• Reduced battery life that may require replacements every few weeks

• Disconnection from Wi-Fi

• Disabled motion sensor

• Eventual loss of control

Instead of a 2nd transformer, a Google Nest Power Connector or c-wire is required to ensure your thermostat gets enough continuous power to work properly. (Available for purchase on the Google Store only in the US & CA.) If available, you can have a trained pro install a Power Connector or c-wire for you. Learn about Nest Pro installation services.

– The Google Nest team